The investigator will generate and analyze hypomorphic, null and cell-specific gene modifications of Pitx2. Specific antibodies will be generated to assess the cell specificity of Pitx2 expression in the pituitary and other organs of intact animals. Several pituitary hormone genes have binding sites for Pitx2. There are three isoforms of Pitx2, two of which are expressed in the pituitary gland (Pitx2a, Pitx2b). The relative activity of each Pitx2 isoform on expression of known target genes will be assessed by transient transfection studies using homologous pituitary cell lines. The effects of ectopic Pitx2a and Pitx2b expression in pituitary corticotropes will also be investigated using both transient transfection and transgenic mice. By combining the approaches of transfection, embryonic stem cell technology mice, the investigator will dissect the contributions of individual cells and individual genes in regulating the normal growth and development of the pituitary.